I know, I found it kind of confusing too at first. Refinery indeed is an umbrella term that describes all these features. (Itch support basically told me that its the inbuild features that are available to every one.) To me it looked like its a program you can specifically opt in as creator, given that there is a special page with "current and future games using refinery". But thats not really how it works it seems, it's just the toolset everyone has access to now.
Yeah it determinately feels like its growing. Support has been so so for me. I didn't get another response when inquiring in more detail about refinery, but there are some chaps who have been very for coming with helping me getting my stuff to work on the Itch app.Kind of a mixed back so far, but I'm helped where I realy need it.